Add sync option on pull to pull all platforms

[dmcgowan]

Adds a new sync parameter on the create image api endpoint which indicates all image resources should be fetched with the image. Requires containerd v1.7.17 with fix in unpacker to support this.

The current version is also introducing the transfer service using the local implementation. The transfer service has the cleaner interface with more options, but still requires some work to get the same progress.

Marking as WIP until progress is fixed. Please comment on the API change and overall approach.

[tianon]

"Sync" seems like a weird name for "pull all platforms" -- it makes sense if your mental model is that the local store is effectively a local registry (which I'm definitely a fan of! https://github.com/tianon/containerd-registry 😂), but I don't think that's a common mental model for it. 🤔

It being a strict boolean also seems good for the short-term need, but haven't we had a lot of pain with other booleans over longer-term, given that they're hard to improve/adjust over time?
(also evidenced by // TODO: Options for which artifacts to pull 👀 do we need to instead spend more time figuring out what ways we want to support filtering images to pull at the API level so we know how "just pull everything" fits into that larger model?)